This invention pertains to communications systems, and particularly to communication system which employ a pilot pattern for functions such as synchronization, channel estimation, fine time of arrival estimation and/or device identification.
In a typical cellular radio system, wireless terminals (also known as mobile terminals, mobile stations, and mobile user equipment units (UEs)) communicate via base stations of a radio access network (RAN) to one or more core networks. The wireless terminals (WT) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with the radio access network. The base station, e.g., a radio base station (RBS), is in some networks also called “NodeB” or “B node”. The base stations communicate over the air interface (e.g., radio frequencies) with the wireless terminals which are within range of the base stations.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN is essentially a radio access network providing wideband code division multiple access for user equipment units (UEs). The radio access network in a UMTS network covers a geographical area which is divided into cells, each cell being served by a base station. Base stations may be connected to other elements in a UMTS type network such as a radio network controller (RNC). The Third Generation Partnership Project (3GPP or “3G”) has undertaken to evolve further the predecessor technologies, e.g., GSM-based and/or second generation (“2G”) radio access network technologies.
The IEEE 802.16 Working Group on Broadband Wireless Access Standards develops formal specifications for the global deployment of broadband Wireless Metropolitan Area Networks. Although the 802.16 family of standards is officially called WirelessMAN, it has been dubbed WiMAX″ (from “Worldwide Interoperability for Microwave Access”) by an industry group called the WiMAX Forum. For further information regarding WiMAX generally, see, e.g., IEEE Standard 802.16e-2005 and IEEE Standard 802.16-2004/Cor1-2005 (Amendment and Corrigendum to IEEE Standard 802.16-2004), “IEEE Standard for local and metropolitan area networks, Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems, Amendment 2: Physical and um Access Control Layers for Combined Fixed and Mobile Operation in License Bands,” Feb. 28, 2006, all of which are incorporated herein by reference in their entireties.
A new standard for mobile broadband is being developed in IEEE 802.16m. The IEEE 802.16m standard utilizes, e.g., orthogonal frequency division multiplexing (OFDM). See, e.g., “IEEE 802.16m System Description Document [Draft]”, IEEE 802.16m-08/003r7, incorporated by reference herein in its entirety.
Orthogonal frequency division multiplexing (OFDM) is a special subset of Frequency Division Multiplex (FDM) and is a multi-carrier modulation scheme. In orthogonal frequency division multiplexing (OFDM), the data is simultaneously encoded over various subcarriers. A data stream is split into N parallel streams of reduced data rate and each parallel stream is transmitted on a separate subcarrier. When the subcarriers have appropriate spacing to satisfy orthogonality (e.g., the subcarriers' frequencies differ from each other by integer multiples of the base (lowest) subcarrier frequency), the carriers are mutually orthogonal to each other and their spectra overlap.
Thus, in an Orthogonal Frequency Division Multiplexing (OFDM) system, the data symbols are modulated onto orthogonal time-frequency units of a time-frequency grid or array as defined by the subcarriers of an OFDM symbol. The duration of an OFDM symbol is usually designed to be short enough so that the propagation channel remains unchanged. Within each OFDM symbol, the available bandwidth is divided into a number of orthogonal subcarriers onto which the above-mentioned data symbols are modulated.
OFDM systems typically use known symbols in the time-frequency plane, also known as pilot symbols. Pilot signal design is important since it facilitates multiple functions necessary for operation of the system such as channel estimation, channel quality feedback, multiple-input multiple-output (MIMO) mode adaptation, fine time of arrival estimation and synchronization among others.
Pilot signals are typically designed using regular patterns or some variations of regular patterns in time and frequency. A proposal for an irregular pilot design based on Costas Arrays was made in J. P. Costas, “um Constraints on Sonar Design and Performance”, in EASCON Conv. Rec., 1975, pp. 68A-68L, which is incorporated herein by reference in its entirety.
Costas sequences have been used in the design of delay-Doppler radar signal. See, e.g., J. P. Costas, “A Study of a Class of Detection Waveforms Having Nearly Ideal Range—Doppler Ambiguity Properties,” Proceedings of the IEEE, Vol. 72, No. 8, August 1984, pp. 996-1009, which is incorporated by reference herein in its entirety. A Costas Sequence {τ0, . . . τL−1} has the special property that for any given n≠0, τm-τm−n are distinct for all m within the range. This property ensures that any time-frequency shifted Costas array has at most one coincidence with the original pattern.
The advantage of using Costas arrays is that, the pilots used for channel estimation may also be used for cell/sector identification. See U.S. patent application Ser. No. 11/292,415, entitled “HOPPING PILOT PATTERN FOR TELECOMMUNICATIONS”; U.S. patent application Ser. No. 11/760,654, entitled “NOVEL SIGNATURE SEQUENCES AND METHODS FOR TIME-FREQUENCY SELECTIVE CHANNEL”; and U.S. patent application Ser. No. 11/760,659, entitled “METHOD AND APPARATUS FOR COMPLEXITY REDUCTION IN DETECTION OF DELAY AND DOPPLER SHIFTED SIGNATURE SEQUENCES”; and U.S. patent application Ser. No. 12/438,623, entitled “DETECTION OF TIME-FREQUENCY HOPPING PATTERNS”; all of which are incorporated herein by reference in its entirety. This enables a reduction in system overhead and increases efficiency. Moreover, the Costas Array provides maximum differentiation between the time-frequency positions used for pilot symbols for various base stations, sectors and antennas.
The existing solutions based on regular patterns or their variations do not provide sufficient differentiation between the pilot patterns of multiple cells/sectors. The existing solution based on the Costas Arrays mainly addresses common pilots (which are to be used by all users), but does not adequately address the design of dedicated pilots (which are to be used only by [e.g., dedicated to] the user receiving the data transmission). Dedicated pilots have more difficult constraints in that good estimation performance based on a small set of pilots is necessary.